"Sometimes bad realities make for good fantasies."
It is reasonable to assume that in any given society, certain sexual desires will be held as taboo. Hypothetically, one could imagine a completely unrestricted society in which anything goes, but this is not realistic. By definition, a society - as opposed to a random conglomerate of independent agents - must have some rules, and it is not inconceivable that some members of that society will have sexual desires that involve the transgression of those rules (especially considering the erotic appeal of transgression). The question that remains is what to do with these people who have taboo desires. Do we condemn them for their thoughts, or make a distinction between desire and behavior? I think the answer depends a lot on our conception of human sexuality.
Currently, we have a very damaged understanding of how sexuality works. We believe that alternative desires arise from warped psychology; and the political nature of the issue precludes real scientific research from being conducted (or considered by the public). Naively, we conclude that only bad people have bad desires, because only bad people could desire bad things. But, unlike behavior, desire is not a choice. An inclination to commit murder, for example, does not operate like sexual arousal to the concept of murder. Yet, our conception of human sexuality presumes that if a person is turned on by murder, they will inevitably seek to commit murder, because of the myth that (especially among men, who are discriminatorily viewed as the only sex that experiences perversion) the sexual impulse trumps all reason.
"Nothing’s villainous if it causes an erection, and the single crime that exists in this world is to refuse oneself anything that might produce a discharge." - The Marquis de Sade, 120 Days of Sodom
But, I say, this is not true. Good people can come to find that they have problematic sexual desires. Yet, being good people, they can still make good choices about what to do with those desires. This is the basic principle behind the BDSM community, and the idea of consensual non-consent. Rape is a horrible crime. But people can become psychologically conditioned (due to factors outside of our control) to respond sexually to the concept of rape. Yet they are not destined to rape or be raped. Provided with a community of like minds, who emphasize the importance of consent, and the power of roleplay to indulge one's fantasies even where desire breaks from reality, a person with problematic sexual desires can learn to indulge them safely and sanely, and go on to lead a satisfied and well-adjusted public life.
In light of this fact, should we be in the habit of condemning people for having sexual desires that are taboo, or for things that most people would find repulsive? Should we isolate and alienate these people, and pound into their heads the idea that they are bad people for having these desires they did not choose? That they are inevitably on a path to destruction, and must be stopped (echoing shades of "precrime") before they have a chance to take others down with them into the pits of debauchery? Should we endeavor to eliminate these undesirables from the population at large through a curriculum of eugenics? All to assuage the moral conscience of a deluded majority that cares more for appearances than results (making public overtures to purity, while harboring dirty secrets of their own), while trampling disadvantaged minorities underfoot?
Or should we, instead, seek to adopt a more humanitarian approach toward human sexuality, and try to foster healthy and balanced attitudes towards sex, where pleasure and good vibes - not shame and isolation - are the goal? To lay a foundation that celebrates human diversity, and grants unlimited freedom to people to use their imaginations unrestricted in the pursuit of happiness. To subject human sexual encounters to the same philosophy of law that governs all other encounters - not to hurt, steal, or deceive, except as agreed upon and desired by the participants, but to otherwise allow people to enjoy themselves and define their own limits, free from institutional stigma. To foster a transparent, supportive community that encourages communication, and welcomes knowledge and education, towards the goal of improving everyone's ability to get exactly what they want, and avoid that which they don't. Shouldn't this be our goal? It is, after all, the aim of sex-positivity.